Ordinal Variables (ordinal + variable)

Distribution by Scientific Domains


Selected Abstracts


Multivariate exploratory analysis of ordinal data in ecology: Pitfalls, problems and solutions

JOURNAL OF VEGETATION SCIENCE, Issue 5 2005
János Podani
Abstract Questions: Are ordinal data appropriately treated by multivariate methods in numerical ecology? If not, what are the most common mistakes? Which dissimilarity coefficients, ordination and classification methods are best suited to ordinal data? Should we worry about such problems at all? Methods: A new classification model family, OrdClAn (Ordinal Cluster Analysis), is suggested for hierarchical and non-hierarchical classifications from ordinal ecological data, e.g. the abundance/dominance scores that are commonly recorded in relevés. During the clustering process, the objects are grouped so as to minimize a measure calculated from the ranks of within-cluster and between-cluster distances or dissimilarities. Results and Conclusions: Evaluation of the various steps of exploratory data analysis of ordinal ecological data shows that consistency of methodology throughout the study is of primary importance. In an optimal situation, each methodological step is order invariant. This property ensures that the results are independent of changes not affecting ordinal relationships, and guarantees that no illusory precision is introduced into the analysis. However, the multivariate procedures that are most commonly applied in numerical ecology do not satisfy these requirements and are therefore not recommended. For example, it is inappropriate to analyse Braun-Blanquet abudance/dominance data by methods assuming that Euclidean distance is meaningful. The solution of all problems is that the dissimilarity coefficient should be compatible with ordinal variables and the subsequent ordination or clustering method should consider only the rank order of dissimilarities. A range of artificial data sets exemplifying different subtypes of ordinal variables, e.g. indicator values or species scores from relevés, illustrate the advocated approach. Detailed analyses of an actual phytosociological data set demonstrate the classification by OrdClAn of relevés and species and the subsequent tabular rearrangement, in a numerical study remaining within the ordinal domain from the first step to the last. [source]


Effects of long-term cyclo-oxygenase 2 selective and acid inhibition on Barrett's oesophagus

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 6 2007
A. LANAS
Summary Background There is an overexpression of cyclo-oxygenase 2 (COX-2) in Barrett's oesophagus (BO). Aim To determine the long-term effect of a COX-2 inhibitor on cellular mechanisms involved in BO. Methods A randomized controlled trial was conducted in BO patients allocated to continue the usual proton pump inhibitor (PPI) alone treatment, or PPI combined with rofecoxib (25 mg/day) for 6 months. Cell proliferation index and COX-2 expression in BO glands was determined in biopsy specimens at baseline and after treatment. Cell apoptosis, cyclin D1, p53 and vascular endothelial growth factor (VEGF) expression was also explored in a subset of patients. Student- t test and the U-Mann,Whitney test were used for quantitative and ordinal variables. Results Of 62 patients, 58 completed the study. A higher proportion of patients on rofecoxib + PPI exhibited a decrease in COX-2 expression compared to those treated with PPI alone, but cell proliferation index was not affected. Unlike PPI alone, rofecoxib + PPI was associated with an increase in the apoptotic cell index, a decrease in p53 cell staining and VEGF expression in mucosal vessels. No effect on low-grade dysplasia or cyclin D1 was observed. Conclusions The addition of rofecoxib to PPI therapy does not affect cell proliferation index in BO cells after 6 months of therapy, but does reduce COX-2 and VEGF expression and increases cell apoptosis. [source]


Associations of factor VIIIc, D-dimer, and plasmin,antiplasmin with incident cardiovascular disease and all-cause mortality

AMERICAN JOURNAL OF HEMATOLOGY, Issue 6 2009
Aaron R. Folsom
To examine the associations of three understudied hemostatic factors,D-dimer, factor VIIIc, and plasmin-antiplasmin (PAP) complex,with incident cardiovascular disease (CVD) and all cause mortality in the Multiethnic Study of Atherosclerosis cohort. Hemostatic factors were measured at baseline in 45,84-year-old patients (n = 6,391) who were free of clinically recognized CVD. Over 4.6 years of follow-up, we identified 307 CVD events, 207 hard coronary heart disease events, and 210 deaths. D-dimer, factor VIIIc, and PAP were not associated with CVD incidence after adjustment for other risk factors. In contrast, each factor was associated positively with total mortality, and D-dimer and factor VIIIc were associated positively with cancer mortality. When modeled as ordinal variables and adjusted for risk factors, total mortality was greater by 33% (95% CI 15,54) for each quartile increment of D-dimer, 26% (11,44) for factor VIIIc, and 20% (4,38) for PAP. This prospective cohort study did not find D-dimer, factor VIIIc, or PAP to be risk factors for CVD. Instead, elevated levels of these three hemostatic factors were associated independently with increased risk of death. Elevated D-dimer and factor VIIIc were associated with increased cancer death. Am. J. Hematol., 2009. © 2009 Wiley-Liss, Inc. [source]


Criminal Behavior in Antisocial Substance Abusers between Five and Fifteen Years Follow-Up

THE AMERICAN JOURNAL ON ADDICTIONS, Issue 1 2007
Mats Fridell PhD
Antisocial personality disorder (ASPD) is one of the most common co-occurring disorders in substance abusers, characterized among other things by a high propensity for criminal actions. A cohort of 125 substance abusers were followed in a longitudinal design. Patients were diagnosed with ASPD at an index treatment episode, interviewed at five-year follow-up, and followed-up through the Swedish criminal justice register by 2005 for the years 1995,2003. ASPD and non-ASPD subjects were compared using Mann Whitney U test for ordinal variables (number of offenses and months in prison) and chi-square tests for categorical variables. A total of 107 were alive by 1995, when the period of observation began. ASPD diagnosed at baseline was related to criminal offenses and incarceration during the follow-up from 5 to 15 years. For most categories, ASPD diagnosis was associated with higher frequency of offense. An ASPD diagnosis based on SCID-II interview made at five-year follow-up was related to the number of offenses but unrelated to incarceration. In a sample of drug abusers, ASPD was associated with high levels of criminal behavior, even years after the diagnosis was given. A diagnosis based on clinical observation during treatment was at least as predictive of criminal behavior as a diagnosis based on a SCID-II interview. [source]


Interobserver Agreement in Assessment of Clinical Variables in Children with Blunt Head Trauma

ACADEMIC EMERGENCY MEDICINE, Issue 9 2008
Marc H. Gorelick MD
Abstract Objectives:, To be useful in development of clinical decision rules, clinical variables must demonstrate acceptable agreement when assessed by different observers. The objective was to determine the interobserver agreement in the assessment of historical and physical examination findings of children undergoing emergency department (ED) evaluation for blunt head trauma. Methods:, This was a prospective cohort study of children younger than 18 years evaluated for blunt head trauma at one of 25 EDs in the Pediatric Emergency Care Applied Research Network (PECARN). Patients were excluded if injury occurred more than 24 hours prior to evaluation, if neuroimaging was obtained at another hospital prior to evaluation, or if the patient had a clinically trivial mechanism of injury. Two clinicians independently completed a standardized clinical assessment on a templated data form. Assessments were performed within 60 minutes of each other and prior to clinician review of any neuroimaging (if obtained). Agreement between the two observers beyond that expected by chance was calculated for each clinical variable, using the kappa (,) statistic for categorical variables and weighted kappa for ordinal variables. Variables with a lower 95% confidence limit (LCL) of , > 0.4 were considered to have acceptable agreement. Results:, Fifteen-hundred pairs of observations were obtained. Acceptable agreement was achieved in 27 of the 32 variables studied (84%). Mechanism of injury (low, medium, or high risk) had , = 0.83. For subjective symptoms, kappa ranged from 0.47 (dizziness) to 0.93 (frequency of vomiting); all had 95% LCL > 0.4. Of the physical examination findings, kappa ranged from 0.22 (agitated) to 0.89 (Glasgow Coma Scale [GCS] score). The 95% LCL for kappa was <0.4 for four individual signs of altered mental status and for quality (i.e., boggy or firm) of scalp hematoma if present. Conclusions:, Both subjective and objective clinical variables in children with blunt head trauma can be assessed by different observers with acceptable agreement, making these variables suitable candidates for clinical decision rules. [source]